Protection of the environment is an increasingly important concern at the present time, not only in politics but also in the economy. Many governments have enacted restrictive environmental regulations relating to the operation of fossil fuel combustion systems. Furthermore there are numerous tax advantages for companies operating environmentally friendly installations or converting their existing systems.
Reducing NOx emissions is one of the factors that play an important role in the burning of fossil fuels.
Since NOx emissions increase considerably at combustion temperatures above 1800°, it is the aim of all reduction measures to keep the combustion temperature below this temperature. Essentially, two measures are known for achieving this aim. In the case of the first measure the combustion takes place substoichiometrically, i.e. the combustion takes place with an excess of air. In this case the increased air mass ensures heat is absorbed in the reaction zone of the combustor and thereby limits the temperature in the combustion chamber to a temperature at which only small quantities of NOx are produced.
The second NOx reduction measure consists in a particularly good mixing of the fuel and the air before the mixture is injected into the combustion chamber. The better the blending of the air/fuel mixture prior to combustion, the lower is the probability that zones in which an increased fuel fraction occurs (hotspots) will form in the combustion chamber. The zones would otherwise lead to local temperature increases in the combustion chamber and consequently to an increase in NOx emissions.
In order to achieve a good mixing of fuel and air, swirlers according to the claims have been used hitherto. A swirler of this kind is disclosed in EP 18 67 925 A1 for example. The swirler comprises a plurality of vanes arranged on a reference circle diameter which, together with a first wall disposed on a first longitudinal end face of the vanes and a second wall disposed on an opposing second longitudinal end face of the vanes, form a flow channel. The air streams through the swirler from an externally located high-pressure side to the internal low-pressure side. The fuel is supplied to the flow channel via injection orifices in one of the two walls as well as in the vanes. In the process the injected fuel mixes with the air streaming through the flow channel, thereby producing a fuel/air mixture which subsequently enters the combustion chamber.